Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
  • G11B5/852—Orientation in a magnetic field
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
  • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
  • G11B5/716—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by two or more magnetic layers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/90—Magnetic feature
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/25—Web or sheet containing structurally defined element or component and including a second component containing structurally defined particles
  • Y10T428/256—Heavy metal or aluminum or compound thereof
  • Y10T428/257—Iron oxide or aluminum oxide
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/26—Web or sheet containing structurally defined element or component, the element or component having a specified physical dimension
  • Y10T428/263—Coating layer not in excess of 5 mils thick or equivalent
  • Y10T428/264—Up to 3 mils
  • Y10T428/265—1 mil or less

Definitions

• This invention relates to a magnetic recording medium and more particularly, it is concerned with an improved magnetic recording medium having an S/N ratio increased in high density recording.
• the recording density as defined above becomes high, the output decrease due to self-demagnetization (decrease of the residual magnetization by a self-demagnetization field acting in a direction to negative the self-magnetization between N and S poles formed by the self residual magnetization, which is increased with the decrease of the distance between the N and S poles) is not so large if the recording wavelength is smaller than the thickness of a magnetic layer, and the high density recording is effective with a recording wavelength of 1-2 microns or less.
• a magnetic tape having a two layer structure using acicular magnetic particles with a large length/width ratio has hitherto been known wherein in the lower layer, the particles are oriented in parallel with the surface of the support and in the upper layer, they are oriented vertically to the surface to thus raise the short wavelength sensitivity.
• the acicular particles tend to fall down to be in parallel with the surface with the decrease of the thickness due to vaporization of a solvent during drying. This tendency is increased with the degree of anisotropy, i.e. with the increase of the length/width ratio.
• a magnetic recording medium comprising a non-magnetic support and two or more magnetic recording layers superposed thereon in which ferromagnetic particles are dispersed in a binder, characterized in that the ferromagnetic particles of the outermost magnetic layer are given a main magnetic anisotropy by a magnetic annealing treatment and the direction of the magnetic anisotropy is vertical to the recording surface.
• the inventors have noticed that particles are given a uniaxial anisotropy by magnetic annealing in addition to the shape anisotropy and this technique is available for a magnetic recording medium with a multilayer structure in such a manner that the direction of the magnetic anisotropy by magnetic annealing be vertical to a recording surface, and have reached the present invention.
• the present invention provides a magnetic recording medium comprising a non-magnetic support and two or more magnetic recording layers containing ferromagnetic particles dispersed in a binder, in which the ferromagnetic particles of the outermost magnetic layer are given a main magnetic anisotropy in the vertical direction to the recording surface by a magnetic annealing treatment.
• the ferromagnetic particles are cubic particles with a length/width ratio of 2 or less.
• ferromagnetic particles are subjected to a magnetic annealing treatment which consists in placing a ferromagnetic powder in a magnetic field at a high temperature and cooling gradually while applying the magnetic field thereto, whereby to give a uniaxial magnetic anisotropy in the direction of the applied magnetic field, as described in Soshin Chikakado: "Kyojiseitai no Butsuri (Physics of Ferromagnetic Substance)" page 254-267, published September, 1959 by Shokabo.
• various materials are known such as ferrites, Fe-Co, Fe-Ni alloys and the like, and in particular, Co-doped ferrites show a more remarkable magnetic annealing effect.
• Those containing Co in a proportion of 0.3 to 30% have a higher coercive force in proportion to the content of Co and exhibit a magnetic annealing effect at a relatively low temperature, e.g. 200°-300° C. or less, whereby the magnetic anisotropy appears under ambient conditions at room temperature.
• the size of a particle to be subjected to a magnetic annealing treatment is preferably 2 microns or less and the shape thereof is not particularly limited.
• the particle size is preferably 0.3 micron or less and the shape thereof is preferably oval to cubic with a length/width ratio of about 1.
• the temperature and period of time for effecting a magnetic annealing treatment depend upon the amounts of Co, Fe ++ and other additives and the history of a product, but in general, they can respectively be determined experimentally so as to increase the squareness ratio (Br/Bm) of BH curve.
• the temperature for magnetic annealing is 50°-300° C., since if lower than 50° C., the merit achieved by the magnetic annealing effect according to the present invention tends to be decreased with the passage of time.
• the magnetic annealing treatment is carried out under powdered state and thereafter, the treated powder is dispersed in a binder, coated and then subjected to an orientation treatment in the vertical direction to the surface.
• the magnetic annealing treatment can be carried out while applying a magnetic field vertical to the surface of a magnetic recording medium after coated and dried.
• the magnetic annealing treatment according to the present invention is preferably carried out under the following conditions:
• cooling speed gradual, e.g. about 1° C./min
• the magnetic orientation treatment of ferromagnetic particles in the vertical direction to a recording surface is effectively carried out in a DC magnetic field by a permanent magnet, electromagnet or solenoid optionally with superposing an AC magnetic field or with using jointly ultrasonic wave.
• the lower magnetic layer of the present invention has a coercive force similar to or less than that of the uppermost magnetic layer and is oriented so as to be magnetized in a recording direction, i.e. longitudinally in general, but circumferentially in the case of a disk-shaped magnetic recording medium.
• the magnetic powder used in the lower layer is so chosen that the reproducing output at a low recording density (such that the minimum unit of recording exceeds approximately the thickness of the upper layer) may be held high.
• particles having a length of more than 0.3 micron and a large length/width ratio are preferably used, but of course, it is possible to use particles which are given a large magnetic anisotropy by the effect of a magnetic annealing treatment and oriented in a recording surface or recording direction. In this case, the particles need not always have a large length/width ratio.
• three or more magnetic recording layers can be provided in the magnetic recording medium of the present invention.
• ferromagnetic particles used in the lower layer of the present invention are ferromagnetic fine powders of ⁇ -Fe 2 O 3 , Co-doped ⁇ -Fe 2 O 3 , Fe 3 O 4 , Co-doped Fe 3 O 4 , Co-doped Fe 3 O 4 , Berthollide compounds of ⁇ -Fe 2 O 3 and Fe 3 O 4 (FeO x : 1.33 ⁇ x ⁇ 1.50), Co-doped Berthollide compounds of ⁇ -Fe 2 O 3 and Fe 3 O 4 (FeO x : 1.33 ⁇ x ⁇ 1.50), CrO 2 , Co-Ni-P alloys, Co-Ni-Fe alloys, Co-Ni-Fe-B alloys, Fe-Ni-Zn alloys, Fe-Mn-Zn alloys, Fe-Co-Ni-P alloys and Ni-Co alloys.
• the ferromagnetic particles used in the outermost layer can be also used in the lower layer
• a non-magnetic binder for dispersing ferromagnetic particles and a support should be made of materials capable of resisting a high temperature, in general, 100° to 300° C. required for a magnetic annealing treatment.
• Suitable binders which can be used in the present invention include hitherto known thermoplastic resins, thermosetting resins and mixtures thereof.
• Suitable thermoplastic resins are those which have a softening point of about 150° C. or lower, a mean molecular weight of about 10,000 to 200,000 and a degree of polymerization of about 200 to 2,000, for example, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, acrylate-acrylonitrile copolymers, acrylate-vinylidene chloride copolymers, acrylate-styrene copolymers, methacrylate-acrylonitrile copolymers, methacrylate-vinylidene chloride copolymers, methacrylate-styrene copolymers, urethane elastomers, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymers, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyral, cellulose derivatives
• thermosetting resins have a molecular weight of about 200,000 or less as a coating solution and when heated after coating and drying, the molecular weight becomes infinity due to reactions such as condensation, addition and the like.
• preferred resins are those which do not soften or melt before the resin thermally decomposes.
• these resins are phenol resins, epoxy resins, polyurethane hardening type resins urea resins, melamine resins, alkyd resins, silicone resins, acryl based reactive resins, epoxy-polyamide resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of methacrylic acid salt copolymer and diisocyanate prepolymers, mixtures of polyesterpolyols and polyisocyanates, ure-formaldehyde resins, mixtures of low molecular weight glycols, high molecular weight diols and triphenylmethane triisocyanates, polyamide resins and mixtures thereof, etc.
• binders can be used individually or in combination with each other and other additives can be added to the binders.
• the mixing ratio by weight of a ferromagnetic powder and a binder is 10 to 400 parts by weight, preferably 30 to 200 parts by weight of the binder to 100 parts by weight of the ferromagnetic powder.
• additives such as dispersing agents, lubricants, abrasives, antistatic agents and the like can be added to the magnetic recording layer.
• Suitable dispersing agents are fatty acids containing about 12 to 18 carbon atoms represented by the general formula R 1 COOH wherein R 1 is an alkyl group containing about 11 to 17 carbon atoms, for example, caprylic acid, capric acid, lauric acid, muristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linolic acid, linolenic acid, stearolic acid and the like; metallic soaps comprising the alkali metal (Li, Na, K etc.) salts or the alkaline earth metal (Mg, Ca, Ba, etc.) salts of the above described fatty acids; and lecithin, etc.
• R 1 is an alkyl group containing about 11 to 17 carbon atoms
• higher alcohols containing about 12 or more carbon atoms and the sulfates thereof can be used.
• These dispersing agents are generally used in a proportion of about 1 to 20 parts by weight per 100 parts by weight of a binder. These dispersing agents are described in Japanese Patent Publication Nos. 28369/1964, 17945/1969 and 15001/1973 and U.S. Pat. Nos. 3,387,993 and 3,470,021.
• Suitable lubricants which can be used in the present invention include silicone oils, carbon black, graphite, carbon black graft polymers, molybdenum disulfide, tungsten disulfide, fatty acid esters produced from a monocarboxylic acid containing about 12 to 16 carbon atoms and a monohydric alcohol containing about 3 to 12 carbon atoms, fatty acid esters produced from a monocarboxylic fatty acid containing about 17 or more carbon atoms and a monohydric alcohol in which the total number of carbon atoms ranges from about 21 to 23 and the like. These lubricants are generally used in a proportion of about 0.2 to 20 parts by weight per 100 parts by weight of a binder.
• Typical abrasive agents which can be used in the present invention include fused alumina, silicon carbide, chromium oxide, corundum, diamond, synthetic diamond, garnet, emery (main component: corundum and magnetite) and the like. These abrasive agents have generally a mean particle size of 0.05 to 5 microns, preferably 0.1 to 2 microns and are generally added in a proportion of 1 to 10 parts by weight to 100 parts by weight of the magnetic powder. Examples of the abrasives are described in Japanese Patent Application No. 26749/1973, U.S. Pat. Nos. 3,007,807, 3,041,196, 3,293,066, 3,630,910 and 3,687,725, British Pat. No. 1,145,349, West German Pat. No. 853,211 and 1,001,000.
• Antistatic agents which can be used in the present invention include electrically conductive powders such as graphite, carbon black and carbon black graft polymers; natural surface active agents such as saponin; nonionic surface active agents such as alkylene oxide based, glycerol based and glycidol based surface active agents; cationic surface active agents such as heterocyclic compounds, e.g.
• alkylamines higher alkylamines, quaternary ammonium salts, pyridine and the like; phosphoniums, sulfoniums and the like; anionic surface active agents containing acid groups such as carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, sulfate groups, phosphate groups and the like; amphoteric surface active agents such as sulfates or phosphates of amino acids, amino sulfonic acids, amino alcohols and the like; etc.
• These surface active agents can be used individually or in combination with each other. These surface active agents are generally used as antistatic agents, but in some cases, they are used for other purposes, for example, for improving dispersibility, magnetic properties and lubricity, or as an auxiliary coating agent.
• Formation of a magnetic recording layer is carried out by dissolving or dispersing the above described composition in an organic solvent and then coating the resulting composition onto a support.
• Suitable materials which can be used for this support are various plastics, for example, polyesters such as polyethylene terephthalate, polyethylene-2,6-naphthalate and the like, polyolefins such as polypropylene and the like, cellulose derivatives such as cellolose triacetate, cellulose diacetate and the like, polycarbonates, etc., and non-magnetic metals, for example, copper, aluminum, zinc, etc.
• a non-magnetic support can have a thickness of about 3 to 100 microns, preferably 5 to 50 microns in the form of a film or sheet, and about 0.5 to 10 mm in the form of a disk or card.
• a cylindrical form such as drum can be used.
• the above described magnetic powder, binder, dispersing agent, lubricant, abrasive agent, antistatic agent and solvent are well blended or kneaded to prepare a coating composition.
• the magnetic powder and other components are charged in a kneading machine simultaneously or separately.
• a magnetic powder is added to a solvent containing a dispersing agent, kneaded for a predetermined period of time, then mixed with other components and kneaded sufficiently to prepare a magnetic coating composition.
• kneading machines are used for the kneading and dispersing, for example, two roll mills, three roll mills, ball mills, pebble mills, trommel mills, sand grinders, Szegvari attriters, high speed impeller dispersing machines, high speed stone mills, high speed impact mills, kneaders, high speed mixers, homogenizers, ultrasonic dispersing machines, etc.
• the kneading and dispersing techniques are described in T. C. Patton, "Paint Flow and Pigment Dispersion", published by John Wiley & Sons (1964) and U.S. Pat. No. 2,581,414 and 2,855,156.
• the foregoing magnetic recording layer can be coated on a support using coating methods such as air doctor coating, blade coating, air knife coating, squeeze coating, dip coating, reverse roll coating, transfer roll coating, gravure coating, kiss coating, cast coating, spray coating and the like, and other coating methods can also be used. These methods are described in "Coating Kogaku (Coating Engineering)", page 253 to 277, published by Asakura Shoten, Tokyo (Mar. 20, 1971).
• Typical organic solvents which can be used in the coating include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and the like; alcohols such as methanol, ethanol, propanol, butanol and the like; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether acetate and the like; ethers and glycol ethers such as diethyl ether, glycol monoethyl ether, glycol dimethyl ether, dioxane and the like; aromatic hydrocarbons such as benzene, toluene, xylene and the like; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene and the like; etc.
• ketones such as
• the thickness of the upper layer and lower layer is suitably determined depending upon the intended use and in general, the upper layer has a thickness of 0.5 to 3 microns, while the lower layer has a thickness of 2 to 5 microns.
• the thickness may be 0.1 to 2 microns.
• the solution M and A were heated at 40° C.
• To the solution A stirred were added the solution M and further the solution OX, and the temperature of the mixture was increased to 80° C.
• the reaction was continued for about 30 minutes to obtain a Co-containing magnetite powder, which was then subjected to a heat treatment at 200° C. in nitrogen atmosphere for 1 hour and treated to 200° C. in a magnetic field of 2000 gauss for 30 minutes, followed by cooling gradually at a rate of 1° C./min.
• a magnetic coating liquid I was prepared according to the following recipe:
• This magnetic coating liquid I was ball milled and well dispersed, coated onto a polyethylene terephthalate base of 22 ⁇ to give a coating thickness of 5 ⁇ on dry base and passed through between poles forming a magnetic field of 800 gauss in the vertical direction, where the coated film was substantially dried by hot air, thus obtaining Sample No. 1.
• This magnetic coating liquid II was coated onto a polyethylene terephthalate base of 22 ⁇ in thickness to give a coating thickness of 4 ⁇ on dry base and subjected in conventional manner to a magnetic orientation in the web in the longitudinal direction. After drying, the coated film was subjected to a calendering treatment to smoothen the surface. The magnetic coating liquid I was then coated onto the smoothened surface to give a thickness of 1 ⁇ on dry base and dried substantially in a vertical magnetic field of 800 gauss to obtain a magnetic tape (Sample No. 2).
• a magnetic coating liquid I' was prepared by the use of the acicular ⁇ -Fe 2 O 3 of the magnetic coating liquid II in the magnetic coating liquid I and coated onto a coated film of the magnetic coating liquid II with a thickness of 4 ⁇ to give a thickness of 1 ⁇ , thus obtaining a magnetic tape (Sample No. 3).
• Br/Bm ratio is a ratio of residual magnetic flux density to saturated magnetic flux density of BH curve measured in the vertical direction to the surface of a magnetic tape by means of a magnetic flux meter of sample vibration type (made by Toei Kogyo Co.)
• a and B are the reproducing outputs of a magnetic tape, A being the output at a short recording wavelength (relative speed of head and tape/signal frequency), i.e. 1 ⁇ and B being a ratio of the output of a signal (3 MHz) in A to the noise level at a point of 2 MHz part by 1 MHz from this signal
• C is the reproducing output at a relatively long recording wavelength, i.e. 100 ⁇ .
• A, B and C are respectively represented by dB unit.
• Sample No. 2 of the present invention is more excellent in all the output properties A, B and C than Sample No. 3 having the two layers in which the magnetic particles of the upper layer are not subjected to magnetic annealing and vertical orientation treatment to a recording surface and in the reproducing output at a relatively long recording wavelength than Sample No. 1 having the single layer in which the magnetic particles are subjected to magnetic annealing and vertical orientation.
• a magnetic coating liquid having the following composition was prepared:
• ferromagnetic iron oxide there were used magnetic powders X, Y and Z, X being the same as used in the magnetic coating liquid I of Example 1 and subjected to the magnetic annealing treatment of Example 1, Y being the same as X but omitting the magnetic annealing treatment and Z being the same acicular iron oxide as used in the magnetic coating liquid II of Example 1.
• compositions were charged in a ball mill and well dispersed to prepare magnetic coating liquids III, IV and V corresponding to the magnetic powder X, Y and Z.
• the thus resulting magnetic coating liquid V was coated onto a support of polyimide film (Kapton-commercial name-) with a thickness of 23 ⁇ to give a thickness of 4 ⁇ on dry base, oriented in the surface and in the longitudinal direction and subjected to a calendering treatment. Then, each of the magnetic coating liquids III and IV was coated thereon to give a thickness of 1 ⁇ on dry base and for comparison, there was prepared a tape which upper layer and lower layer are of the magnetic coating liquid IV.
• polyimide film Kerpton-commercial name-
• Sample Nos. 4 and 5 of the present invention are superior to Sample No. 6 having the single magnetic layer with respect to the output property at a longer recording wavelength, and it is apparent from comparison with Sample No. 7 that Sample Nos. 4 and 5 give better output properties by effecting a magnetic annealing treatment after tape making.

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• Paints Or Removers (AREA)
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• Manufacturing Of Magnetic Record Carriers (AREA)

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• 1981
  • 1981-05-07 JP JP56067641A patent/JPS57183630A/ja active Granted
• 1982
  • 1982-05-07 DE DE19823217211 patent/DE3217211A1/de active Granted
• 1984
  • 1984-03-05 US US06/585,020 patent/US4513054A/en not_active Expired - Lifetime

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